The present invention relates generally to hot melt adhesive applicators and, more particularly, to hot melt adhesive applicators of a slot die type.
Hot melt adhesive applicators typically have an air supply provided from a source to a pneumatic adhesive applicator valve located on a service block from which hot melt adhesive under pressure is dispensed. As depicted in FIG. 4, the adhesive applicator valves are operated by external solenoids 24 that control the ON-OFF positions of the pneumatic adhesive applicator valves and thus the ON-OFF dispensing of adhesive. The external solenoids 24 are typically spaced a considerable distance away from the adhesive service block 19 by means of long air tubes 26 and 28 that are used to avoid exposure to the heat generated by the service block which is typically heated to temperatures in a preferred range of 375-450xc2x0 F. Accordingly, and disadvantageously, the air supply path both from the external solenoids 24, through the air tubes, 26, 28 and then to and through air passages within the service block 19 and finally to the adhesive applicator valves 34, can become so long as to create a time delay that undesirably delays operation by increasing the response time of the applicator valves, causing inconsistencies in the discharge and pattern of adhesive dispensed. This is due to the time needed for the air to fill the entire air path to a pressure suitable for operating the adhesive valves.
It is accordingly one object of the invention to minimize the response time for air to be supplied from the external solenoids to the adhesive applicator valves.
Another object is to improve the reliability in use of hot melt adhesive applicators.
As is common in such applicators, the hot melt adhesive is discharged under pressure through a discharge opening, such as a slot, formed in a die block mounted to the service block. The die block utilizes a separate heat source from that of the service block to allow for better control over the adhesive distribution process or pattern. However, since the die block is mounted directly to the service block, it is difficult to maintain the integrity of the separate heat zones and this also adversely effects control of the adhesive process/pattern.
Accordingly, still another object is to maintain the integrity of the separate heat zones of the service block and die block to allow for better control of the adhesive process/pattern.
A hot melt adhesive applicator, in accordance with the present invention, comprises an adhesive service block having at least one adhesive applicator or dispenser valve module attached thereto for controlling the supply of adhesives under pressure. A service block heater is connected to heat the service block and the adhesive therein. At least one solenoid operated air valve is operatively connected to the service block assembly for supplying air from a source through appropriate air passages to operate the adhesive applicator valves between open and closed positions to control the flow of adhesive from the service block and into a die block assembly connected to the service block. The die block assembly includes at least one discharge opening of desired shape, such as a slot in the case of a slot die type applicator, from which the adhesive is discharged under pressure.
In accordance with the present invention, contrary to existing applicators, the air valve assembly is mounted directly to the service block as opposed to remotely through air tubes. This direct mounting arrangement eliminates the intermediary of any air supply tubes and minimizes the response time for the air to react and fill the air line chamber that communicates with the adhesive service block and ultimately with the applicator valve. This advantageously decreases the response time of the applicator valve operation.
The air valve assembly is preferably mounted to a valve base manifold, preferably by attachment to an upper surface thereof. An insulation element extends between the manifold and the service block to shield the air valve from excessive heat generated by the service block during operation. Both the valve base manifold and the valve insulator element are formed with air passageways that permit communication between the air valves and the air line chamber formed in the service block.
More specifically, the insulation element has upper and lower surfaces in which the upper surface is in direct contact with a lower surface of the valve base manifold and the lower surface of the insulator is in direct contact with an upper surface of the service block assembly. In this manner, the air flow path between the outlet of the air valve and inlet opening(s) in the air line chamber formed in the service block is defined solely by the thickness of the valve base manifold and the insulation element.
In accordance with a unique feature of the preferred embodiment, the upper surface of the service block assembly is formed with a recess in which is received the insulation element. This recess operates to shorten the air flow path as measured between the air valve outlet and an air inlet opening formed in the upper surface of the air line chamber within the recess. In this preferred embodiment, the insulation element has a thickness equal to the depth of the recess.
In accordance with another unique feature of the preferred embodiment, the insulation element is preferably formed with one or more cutouts or notches that extend the full height of the insulation element in order to reduce the surface area contact between the heated service block and the air valve block. In other words, air acts as an insulator between the service block and air in the cutout area or openings defined between the opposing surfaces of the respective blocks.
In accordance with another feature of this invention, a separate thermal insulation element is positioned between the bottom service of the adhesive service block and the upper surface of the die block. Suitable air passageways are provided through this insulation element to enable hot melt adhesive to be discharged from the service block to the die block assembly. The feature of a separate insulation element between these blocks allows for better control of the process/adhesive pattern by maintaining the integrity of the separate heat zones for the service block and the die block.
The die block is further formed with an internal elongate groove in communication with the air passageways through which hot melt adhesive is applied to a point of application. Preferably, the hot melt groove is polished to allow for a sharper adhesive shut off.
Another feature of this invention involves the use of pins in predetermined adjacent locations along the hot melt groove that are adapted to engage openings formed in a clamp that is clamped a to cover the hot melt groove. The feature of providing location pins between the clamp and groove allows for a rapid reattachment of the clamp to the die block assembly following clamp removal for better access and cleaning of the hot melt groove.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as a restrictive.